1. Field of the Invention
This invention relates to a mechanically processed konjac flour that hydrates more rapidly than native (unprocessed) konjac flour and methods for its production including [a] moistening native konjac flour to plasticize it and then milling it to form a flake, followed by grinding of the flake; and [b] cryogenic grinding of dry native konjac flour.
2. Statement of Related Art
Konjac (Amorphophallus konjac) is a plant whose tuber is the source of a well-known foodstuff in China and Japan, namely konjac flour. This flour contains a variety of insoluble materials as well as a major amount of desirable water-soluble substances. When dispersed in water, it forms a highly viscous sol of soluble polysaccharides. The principal soluble constituent is glucomannan, a polysaccharide comprised of D-glucose and D-mannose, which is useful as an ingredient in various foodstuffs, as well as in industrial applications such as films, oil drilling fluids, and paints.
Konjac flour is made by slicing konjac tubers into thin slices, drying, then grinding in a very low speed grinder to break the "tachiko" matrix away from the glucomannan-containing granulets or "sacs". A winnowing (i.e.--air classification) separates the larger, more dense sacs from the tachiko dust.
There are numerous impurities in native konjac flour, including insoluble starches, cellulose, and nitrogen-containing materials, including proteins, many of which impurities constitute the "sacs" which encapsulate the konjac flour in the tuber. These sacs are small, oblong, and lens shaped and are as large as 0.5 mm in length. The size of the sac is believed to vary with the species of konjac, and/or with the age of the plant before harvest. Because of its relatively large sacs, native konjac flour has excellent dispersibility in water, but it takes a long time for the maximum viscosity of an aqueous sol to be reached, usually requiring heating and agitation. Stated in another way, the hydration rate of native konjac flour in room temperature or cool water is relatively slow. This slow hydration is a problem for many uses of native konjac flour, particularly those which employ continuous flow production. To speed up the hydration rate generally requires a reduction in particle size. However, even in a conventional cold mill (which would be the mill of choice to those skilled in the art), grinding causes the konjac flour to degrade as evidenced by its turning brown and smelling burnt, and importantly, also causes a large reduction in attainable viscosity.
Japanese published patent application 63-185345 discloses adding 3 to 20 parts by weight (pbw) of water to 1 pbw of konjac flour to allow swelling of the konjac flour to blocks of sol. To these blocks are added at least 20 wt % alcohol, and they are then wet-ground in what appears to be a high speed blender.
Japanese published patent application 55-92667 discloses freezing sliced and dried konjac tubers in liquid nitrogen and then grinding them to a fine powder in a gaseous nitrogen atmosphere at -50.degree. C. or below, for the purpose of preserving its flavor, fragrance and resilient texture.
U.S. Pat. No. 3,928,322 discloses a classical laboratory method for obtaining small amounts of pure carbohydrates, in particular the glucomannan from konjac flour. Konjac flour is made into an aqueous sol, filtered, the filtrate dialyzed against water, and then lyophilized to recover the solids.